1. Field of the Invention
The present invention generally relates to a fuel injection control system for a cylinder injection type internal combustion engine also known as the direct injection type internal combustion engine. More particularly, the invention is concerned with a fuel injection control system for controlling the fuel injection into the cylinders of the cylinder injection type engine so that a catalyst contained in a catalytic converter disposed in an exhaust gas pipe of the engine can be speedily heated to a light-on temperature, i.e., temperature at which the catalyst begins to be activated in a starting phase of the engine operation.
2. Description of Related Art
In general, a three way catalytic converter is used for purifying an exhaust gas of an internal combustion engine which hereinafter will also be referred to simply as the engine. In this conjunction, it is noted that when the temperature of the catalyst is lower than the light-on temperature as in the case of the cold start of the engine where the engine is stored from a low temperature state, the exhaust gas components such as HC, CO and the like are discharged to the atmosphere without being trapped by the catalytic converter. With a view to coping with this problem, there have already been proposed various measures for promoting speedily the purifying performance or efficiency of the catalytic converter. By way of example, according to one approach, a heater device is installed in the exhaust gas pipe of the engine for heating the catalyst in order to realize high purification efficiency or performance of the catalytic converter as early as possible in the start phase of the engine operation.
As another attempt for heating the catalyst to a desired temperature or light-on temperature, there is disclosed in Japanese Unexamined Patent Application Publication No. 183922/1992 a fuel injection control system for a cylinder injection type spark ignition engine equipped with a temperature sensor for a catalytic converter. The fuel injection control system is so designed that an additional fuel injection is effectuated during an expansion or exhaust stroke for allowing the exhaust gas admixed with the additionally injected fuel to undergo combustion within the exhaust gas pipe with a view to heating the catalyst up to a desired temperature or light-on temperature.
The conventional catalyst heating systems however suffer from a problem that high cost is involved due to need for installation of a heater device in the exhaust gas pipe for raising the temperature of the catalyst or need for installation of a temperature sensor and a second spark plug within the exhaust gas pipe on the way to the exit thereof.